
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
    <!-- 1. 安装 vue-router 路由模块 -->
    <script src="https://cdn.bootcss.com/vue-router/3.1.3/vue-router.js"></script>
    <title>Document</title>
</head>
<body>
    <div id="app">
        <input type="text" v-model="firstname" >+
        <input type="text" v-model="lastname" >=
        <input type="text" v-model="fullname">
    </div>


    <script>
        var vm = new Vue({
            el: '#app',
            data: {
                firstname: '',
                lastname: '',
                fullname: ''
            },
            methods: {
            },
            watch:{
                // 使用这个属性，可以监视data中指定数据的变化，然后触发这个watch中对应的function处理函数
                'firstname':function(newVal,oldVal){
                    // console.log('监视到了firstname变化')
                    // this.fullname = this.firstname + '-' + this.lastname
                    // console.log(newVal,oldVal)
                    this.fullname = newVal + '-' + this.lastname
                },
                'lastname':function(newVal){
                    this.fullname = this.firstname + '-' + newVal
                }
            }
        });
    </script>
</body>
</html>